Disk drive determining a head-switch preheat period used to format a disk

1. A disk drive comprising:

(a) a disk comprising a plurality of tracks, wherein each track comprises a plurality of data sectors;

(b) a plurality of heads; and

(c) control circuitry operable to:

select one of the heads to write a test pattern to the disk;

preheat the selected head for a preheat period;

read the test pattern from the disk using the selected head to generate a read signal;

determine a head-switch preheat period for the selected head in response to the read signal; and

format the disk in response to the head-switch preheat period.

2. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

(a) measure a fly-height of the selected head from the read signal; and

(b) determine the head-switch preheat period in response to the measured fly-height.

3. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

(a) switch from a second one of the heads to the selected head during a head-switch operation;

(b) preheat the selected head for the head-switch preheat period; and

(c) access a data sector using the selected head after the head-switch preheat period and within a single revolution of the disk.

4. The disk drive as recited in claim 1 , wherein the control circuitry is operable to format the disk by mapping a logical block address to a physical block address corresponding to at least one of the data sectors.

5. The disk drive as recited in claim 4 , wherein:

(a) the disk drive further comprises a first disk surface and a second disk surface; and

(b) the control circuitry is further operable to:

map a first and second consecutive logical block address;

map the first logical block address to a first physical block address corresponding to at least one of the data sectors on the first disk surface; and

map the second logical block address to a physical block address corresponding to at least one of the data sectors on the second disk surface, wherein the first physical block address is separated from the second physical block address by a distance corresponding to the head-switch preheat period.

6. The disk drive as recited in claim 1 , wherein the control circuitry is further operable to:

(a) adjust the preheat period for preheating the head;

(b) reread the test pattern from the disk using the selected head to generate a second read signal; and

(c) determine the head-switch preheat period in response to the read signal and the second read signal.

7. The disk drive as recited in claim 6 , wherein:

(a) the disk further comprises a plurality of servo sectors; and

(b) the control circuitry is further operable to adjust the preheat period by an interval corresponding to the delay between reading each servo sector.

8. The disk drive as recited in claim 2 , wherein the control circuitry is operable to extrapolate the head-switch preheat period from the measured fly-height.

9. The disk drive as recited in claim 6 , wherein the control circuitry is operable to extrapolate the head-switch preheat period from the read signal and the second read signal.

10. A method of operating a disk drive, the disk drive comprising a disk including a plurality of tracks, wherein each track comprises a plurality of data sectors, the disk drive further comprising a plurality of heads, the method comprising the steps of:

(a) calibrating a head-switch preheat period for a selected one of the heads by:

writing a test pattern to the disk using the selected head;

preheating the selected head for a preheat period;

reading the test pattern from the disk using the selected head to generate a read signal; and

determining a head-switch preheat period for the selected head in response to the read signal; and

(b) formatting the disk in response to the head-switch preheat period.

11. The method as recited in claim 10 , further comprising the steps of:

(a) measuring a fly-height of the selected head from the read signal; and

(b) determining the head-switch preheat period in response to the measured fly-height.

12. The method as recited in claim 10 , further comprising the steps of:

(a) switching from a second one of the heads to the selected head during a head-switch operation;

(b) preheating the selected head for the head-switch preheat period; and

(c) accessing a data sector using the selected head after the head-switch preheat period and within a single revolution of the disk.

13. The method as recited in claim 10 , wherein the step of formatting the disk comprises the step of mapping a logical block address to a physical block address corresponding to at least one of the data sectors.

14. The method as recited in claim 13 , wherein:

(a) the disk drive further comprises a first disk surface and a second disk surface; and

(b) the step of formatting the disk comprises the steps of:

mapping a first logical block address to a first physical block address corresponding to at least one of the data sectors on the first disk surface; and

mapping a second logical block address to a physical block address corresponding to at least one of the data sectors on the second disk surface, wherein:

the first and second logical block addresses are consecutive; and

the first physical block address is separated from the second physical block address by a distance corresponding to the head-switch preheat period.

15. The method as recited in claim 10 , further comprising the steps of:

(a) adjusting the preheat period for preheating the head;

(b) rereading the test pattern from the disk using the selected head to generate a second read signal; and

(c) determining the head-switch preheat period in response to the read signal and the second read signal.

16. The method as recited in claim 15 , wherein:

(a) the disk further comprises a plurality of servo sectors; and

(b) the preheat period is adjusted by an interval corresponding to the delay between reading each servo sector.

17. The method as recited in claim 11 , further comprising the step of extrapolating the head-switch preheat period from the measured fly-height.

18. The method as recited in claim 15 , further comprising the step of extrapolating the head-switch preheat period from the read signal and the second read signal.